Ever since Ada Lovelace (https://en.wikipedia.org/wiki/Ada_Lovelace) wrote the first algorithm for Analytical Engine (https://en.wikipedia.org/wiki/Analytical_Engine) in the 19th century and Alan Turing (https://en.wikipedia.org/wiki/Alan_Turing) formalized the concepts of algorithm and computation via the Turing machine (https://en.wikipedia.org/wiki/Turing_machine), software has gone through multiple phases in its evolution, both in terms of how it is designed and how it is made available to its end users. The earlier software was designed to run on a single machine in a single environment, and was delivered to its end users as an isolated standalone entity. In the early 1990s, as the focus shifted to application software, the industry started exploring various software architecture methodologies to meet the demands of changing requirements and underlying environments. One of the software architectures that was widely adopted was multitier architecture, which clearly separated the functions of data management, business logic, and presentation. When these layers were packaged together in a single application, using a single technology stack, running as a single program, it was called a monolithic architecture, still in use today.
With the advent of the internet, software started getting offered as a service over the web. With this change in deployment and usage, it started becoming hard to upgrade and add features to software that adopted a monolithic architecture. Technology started changing rapidly and so did programming languages, databases, and underlying hardware. Companies that were able to disintegrate their monolithic applications into loosely-coupled services that could talk to each other were able to offer better services, better integration points, and better performance to their users. They were not only able to upgrade to the latest technology and hardware, but also able to offer new features and services faster to their users. The idea of disintegrating a monolithic application into loosely-coupled services that can be developed, deployed, and scaled independently and can talk to other services over a lightweight protocol, was called microservices-based architecture (https://en.wikipedia.org/wiki/Microservices).
Companies such as Netflix, Amazon, and so on have all adopted a microservices-based architecture. If you look at Google Trends in the preceding screenshot, you can see that the popularity of microservices is rising day by day, but this doesn't mean that monolithic applications are obsolete. There are applications that are still suited for monolithic architecture. Microservices have their advantages, but at the same time they are hard to deploy, scale, and monitor. In this chapter, we will look at both monolithic and microservices-based architectures. We will discuss when to use what and also talk about when and how to migrate from a monolithic to a microservices-based architecture.
